How to convert 2 word Values to Float value (in 32 bit big endian format) in Machine Expert (M251 PLC)

[krishnamodi123]

Hello,

I am using M251 PLC to read data of Master Pact MTZ and Compact NS breakers (both status and measurement signal). Measurement signals like current, voltage, etc. getting in word format (2 words for one signal). I need to covert this 2 word values to Float value (in 32 bit big endian format) in PLC logic to display HMI but couldn't found any block in Machine expert.

In Modscan32, I am getting correct value in swapped float. 

In Machine Expert, I tried  to convert values from %MW0 and %MW1 to %MD0 (as a REAL and DWORD) but not get correct result as in ModScan32.

Kindly advice how to read float value (in big endian format) in Machine expert. Thanks

[Bastian_Schmitz]

Hi,

I you could create a function like that (copied from OSCAT) (OSCAT page)

FUNCTION DW_TO_REAL : REAL
VAR_INPUT
	X : DWORD;
END_VAR
VAR
	pt : POINTER TO REAL;
END_VAR

(*
version 1.0	18. apr. 2008
programmer 	hugo
tested by		tobias

this function converts a DWORD to REAL in a bitwise manner.
*)

(* @END_DECLARATION := '0' *)
pt := ADR(X);
DW_TO_REAL := pt^;

(* revision history
hm	18. apr. 2008
	original version

*)
END_FUNCTION

[johnabraham1122]

To convert two-word values to a float in 32-bit big-endian format in Machine Expert (M251 PLC), follow these steps:

1. Combine the two words into a 32-bit value.
2. Swap the byte order to convert it to big-endian format, if necessary.
3. Use the WORD_TO_DWORD function to merge the words, then apply TO_REAL to convert the DWORD to a float.

Ensure the byte ordering is handled correctly to get accurate results.

[krishnamodi123]

Hi John,

Thank for your reply on my query.

I already tried this. WORD_TO_DWORD block combining 2 word value and make DWORD. TO_REAL block only changing datatype from DWORD to REAL, not converting DWORD to FLOAT value.  

[krishnamodi123]

Hi Bastian,

Thanks for sharing. I will test with this and let you know.

[Obraysingh1122]

To convert two 16-bit word values into a 32-bit float in big-endian format in Machine Expert (M251 PLC):

1. Combine the Words: Use a bitwise operation or a function block to merge the two 16-bit words into a 32-bit variable. Ensure the word order matches the big-endian format.

   • Example: CombinedValue := (Word1 * 16#10000) + Word2;

2. Type Casting: Use the type casting function to convert the combined 32-bit value to a REAL type.

   • Example: FloatValue := TO_REAL(CombinedValue);

3. Verify: Ensure the endianess and value alignment match your system’s requirements. Use a debugger or monitor the variable to confirm correctness.

[krishnamodi123]

Thanks @Obraysingh1122  for sharing a solution. It might will work but I didn't tested this way. Please check my following reply which I implemented and worked perfectly fine on site.

[krishnamodi123 · Accepted solution]

Hi,

Thank you @Obraysingh1122 , @johnabraham1122  and @Bastian_Schmitz  for your reply on this case.

Kindly find below link which is explaining the easiest way to convert 2 word Values to Float value (in 32 bit big endian format).

https://www.youtube.com/watch?v=JPJrG8t_5GA

There is a video made on SoMachine (old version of MachineExpert) in the link. I did the same way in Machine Expert and it worked.

Also,  explaining below as a Example for everyone:

%MW0     %MD0 (need to use Data Type "Real")

%MW1

%MW2     %MD1

%MW3

.

.

.

%MW100     %MD50

%MW101